EP1326198B1 - Verfahren und Vorrichtung zur Beleuchtungserkennung zur Verwendung bei LED-Druckbalken - Google Patents

Verfahren und Vorrichtung zur Beleuchtungserkennung zur Verwendung bei LED-Druckbalken Download PDF

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Publication number
EP1326198B1
EP1326198B1 EP02028810.6A EP02028810A EP1326198B1 EP 1326198 B1 EP1326198 B1 EP 1326198B1 EP 02028810 A EP02028810 A EP 02028810A EP 1326198 B1 EP1326198 B1 EP 1326198B1
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EP
European Patent Office
Prior art keywords
printbar
light emitting
emitting diode
light
photodetector
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired - Fee Related
Application number
EP02028810.6A
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English (en)
French (fr)
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EP1326198A3 (de
EP1326198A2 (de
Inventor
Patrick Y. Maeda
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Xerox Corp
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Xerox Corp
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Filing date
Publication date
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Publication of EP1326198A2 publication Critical patent/EP1326198A2/de
Publication of EP1326198A3 publication Critical patent/EP1326198A3/de
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Publication of EP1326198B1 publication Critical patent/EP1326198B1/de
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Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
    • B41J—TYPEWRITERS; SELECTIVE PRINTING MECHANISMS, i.e. MECHANISMS PRINTING OTHERWISE THAN FROM A FORME; CORRECTION OF TYPOGRAPHICAL ERRORS
    • B41J2/00—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed
    • B41J2/435—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed characterised by selective application of radiation to a printing material or impression-transfer material
    • B41J2/447—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed characterised by selective application of radiation to a printing material or impression-transfer material using arrays of radiation sources
    • B41J2/45—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed characterised by selective application of radiation to a printing material or impression-transfer material using arrays of radiation sources using light-emitting diode [LED] or laser arrays
    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06K—GRAPHICAL DATA READING; PRESENTATION OF DATA; RECORD CARRIERS; HANDLING RECORD CARRIERS
    • G06K15/00—Arrangements for producing a permanent visual presentation of the output data, e.g. computer output printers
    • G06K15/02—Arrangements for producing a permanent visual presentation of the output data, e.g. computer output printers using printers
    • G06K15/12—Arrangements for producing a permanent visual presentation of the output data, e.g. computer output printers using printers by photographic printing, e.g. by laser printers
    • G06K15/1238—Arrangements for producing a permanent visual presentation of the output data, e.g. computer output printers using printers by photographic printing, e.g. by laser printers simultaneously exposing more than one point
    • G06K15/1242—Arrangements for producing a permanent visual presentation of the output data, e.g. computer output printers using printers by photographic printing, e.g. by laser printers simultaneously exposing more than one point on one main scanning line
    • G06K15/1247—Arrangements for producing a permanent visual presentation of the output data, e.g. computer output printers using printers by photographic printing, e.g. by laser printers simultaneously exposing more than one point on one main scanning line using an array of light sources, e.g. a linear array

Definitions

  • Printbars are used in printer systems to identify regions on a paper in which a marking material, such as a toner, is to be deposited.
  • Modem printers often use an array of LEDs on a printbar to mark areas on which to deposit the toner. Each area identified by an LED corresponds to a "pixel" of deposited toner. For an ideal printed image, these pixels should be of uniform in size.
  • each LED on a printbar outputs an intensity that is similar to other LEDs on the printbar.
  • the LED printbars are corrected for non-uniformities between different LEDs in the printbar.
  • each LED in the printbar starts aging at a different rate.
  • the different rates of aging and other changes to the LEDs and the drive systems results in a slow deterioration of printer output as non-uniformities increases in time causing more uneven print results.
  • service personnel are typically called to replace the printbar.
  • EP-A-0310266 describes recalibration for LED array.
  • a method of recalibrating an LED print head comprises providing a photodetector array for detecting the intensity of illumination of each LED, comparing the actual intensity with a desired value and adjusting the level of current applied to the LED array until the actual and desired values correspond, at which time a memory storing the current levels to be applied to the diode array is updated.
  • US-A-4588883 describes monolithic devices formed with an array of light emitting diodes and a detector.
  • An array of light emitting diodes are fabricated in the substrate of a monolithic device. Each diode, when forward biased, produces output light which is emitted from the device and subsurface light which is transmitted through the substrate.
  • a single detector is fabricated in the substrate and detects subsurface light from any forward biased light emitting diode of such array. In response to such subsurface light, the detector produces a signal which is representative of the intensity of output light emitted from the device by such forward biased light emitting diode.
  • Figure 1 shows a printbar 104 as used in a printer system 100.
  • the printbar receives a signal from a source of images, such as a computer 108.
  • the printbar is moved over a photoreceptor plane 112 that receives the light output of the printbar and generates an electrical charge at each point that receives light from a LED.
  • the output of the LEDs is adjusted to such that the light output of the printbar corresponds to a line of an image.
  • a charge pattern is created on the photoreceptors that corresponds to the image to be printed.
  • a marking material source 116 deposits a marking material such as a toner over the photoreceptor plane 112. The marking material adheres to the charged areas of the photoreceptor plane. Heat from a heat source 116 melts the marking material causing adhesion of the marking material to substrate 120, such as paper, that receives the marking material.
  • Figure 2 shows a cross section of one embodiment of printbar 104.
  • a printbar housing 216 and printbar cover 220 support a lens array 224.
  • Lens array 224 is typically a Selfoc Lens array (SLA) that images the light output 228 of LED chips 212 onto photoreceptors in a photoreceptor plane 232.
  • SLA Selfoc Lens array
  • the photoreceptors develop a charge according to the intensity of the light received from LED chips 21.
  • the charge is transferred to a substrate to be marked.
  • the charge attracts marking material deposited on the substrate to be marked.
  • SLA Selfoc Lens array
  • driver circuits also control the individual drive current to each LED element.
  • the drive current to each LED is adjusted to correct for non-uniform light output from the different LEDs in the printbar.
  • the non-uniform outputs typically result from slight differences in LED parameters that occur during the fabrication process. For example some LEDs may have slightly thicker active regions than other LEDs. Before correction, these non-uniformities typically result in a 20 to 30% variation in light intensity output among different LED chips at a given current input. Even when differences in process parameters are minimized by forming different LEDs on the same chip, the different LEDs within the same chip typically still have a 5 to 10% variation in light intensity at a given input current.
  • each LED typically corresponds to a pixel.
  • the toner deposited per pixel is a function of the LED output corresponding to the pixel. Relatively minor variation of even 5 to 10% can result in a noticeable decline in print quality because the human eye is very sensitive to intensity differences over small distances.
  • each driver circuit is also adjusted to correct for the variations.
  • the output of each LED is measured at the SLA image plane.
  • the output of the driver circuit is then adjusted to bring the light intensity output by each LED to a certain predetermined value within the illumination uniformity specification (typically within 1% to 2.5% of a desired intensity value).
  • a calibration current the amount of drive current used to achieve the correct illumination level, is measured and stored.
  • Detector 236 is typically a photodetector that outputs a current, the current being a function of the number of photons (light intensity) above a certain wavelength that reaches the photodetector.
  • a detector match current output by detector 236 when the LED receives a calibration current that results in the detector outputting the desired intensity of light in the SLA image plane is stored in memory. The output of detector 236 will be used for adjustments to the LED in the field.
  • each LED may output different intensities that correspond to the different gray levels of a pixel being printed.
  • the adjustment in intensity is achieved by scaling the driver circuit output current.
  • the actual current received by the LED to print a pixel is thus a scaling of the calibrated current. For example, when a pixel darkness is 50% of the darkest printed pixel, a scaling factor of 50% is multiplied to the calibrated current corresponding to the LED.
  • the scaling factor is the same for all LEDs, only the calibration current differs from pixel to pixel.
  • the LED output at a given driver current usually declines.
  • the rate of decline of different LEDs in the printbar is not uniform.
  • the LED printbar is replaced even though the LEDs may still have a significant period of useful life.
  • a LED printbar can range in price from $100 to $2,000, thus replacing a LED printbar with significant potential remaining life is a large waste of resources.
  • the invention avoids such replacement by periodically recalibrating the printbar using the stored photodetector outputs. The recalibration process using the photodetector is described in the flow chart and description accompanying Figure 8 .
  • Figure 2 shows in an example not forming part of the invention a single detector 236 corresponding to each LED, in order to save on fabrication costs, it is possible to implement the system of the present invention using fewer discrete photodetectors.
  • Figure 3 shows in an example not forming part of the invention using a discrete photodetectors 300, 304, 308, each photodetector corresponding to a LED chip such as LED chip 312 which corresponds to photodetector 300.
  • Each LED chip such as LED chip 312 includes a plurality of LEDs such as LED 316, 320, 324.
  • Alternate examples may be implemented that use one discrete photodetector for every two or more LED chips.
  • reducing the number of discrete detectors increases the solid angle from which light will be received from associated LEDs because the LEDs will be spread over a wider area.
  • the radiation pattern output by each LED may not be uniform in different directions, thus LEDs directly under the detector may provide more accurate reading relating to the decrease in output in the photoreceptor plane then LEDs located a significant distance off axis of the detector.
  • the number of photodetectors should be kept sufficient such that the detection of LED output occurs over a reasonable dynamic range.
  • a strip photodetector 404 runs along the printbar 408 parallel to the series of LEDs. The output of each LED can then be individually measured by keeping all LEDs off and switching only one LED on at a particular point in time. The output of strip photodetector 404 is then measured with the only one LED on.
  • Figure 2 shows photodetector 236 mounted directly to the cover of the printbar, alternate locations for the photodetector are also possible.
  • the position on the cover is ideal for receiving light from the LED, however, fabrication may be simplified by mounting the detector on the circuit board as shown in Figure 5 .
  • a driver circuit 504 mounted on printed circuit board 508 provides power to a LED 512 on LED chip 516.
  • Light 520 output from LED 512 is focused by a lens array 524 onto a photoreceptor plane 528.
  • significant light is also reflected from printbar cover 532 as well as printbar housing 536. The reflected light is detected by a photodetector 540 mounted on printed circuit board 508.
  • Figure 6 shows in an example not forming part of the invention the use of a plurality of discrete photodetectors 604, 608, 612 mounted on a printed circuit board adjacent to LED chips 616, 620, 624.
  • the number of photodetectors may be reduced such that a single discrete photodetector can correspond to several LED chips.
  • a single strip photodetector 704 running parallel to a series of LED chips 708, 712, 716 is used to detect the output of the LED chips.
  • Figure 8 is a flow chart describing the procedures used to readjust the calibration current after the printbar has been in use for a period of time. Blocks of the flowchart correspond to the initial set up of the system usually done during assembly of the printbar. Blocks of the flowchart correspond to recalibration of the printbar after a period of printing.
  • the light output from a LED is detected at a photoreceptor plane.
  • the light from the LED is compared to a desired reference light intensity in block 808.
  • the reference light intensity is the same for all LEDs on the printbar. If the light output by the LED exceeds the reference light intensity, the current provided by the driver circuit is reduced in block 812. If the light output by the LED is less then the reference light intensity, the current provided by the driver circuit is increased in block 816.
  • the calibration current provided by the driver circuit is stored in a memory location in block 820 for future reference. The driver current stored in the memory location is the maximum current provided by the driver circuit to the LED.
  • the output of a photodetector typically a detector match current, is also recorded. The detector match current is the output of the photodetector when the LED outputs the reference light intensity at the photoreceptor plane.
  • the printbar is installed inside the printer.
  • the printbar is subject to normal use in block 832.
  • Such normal use may include, but is not limited to receiving a signal from an imaging source such as a computer and causing the printbar to illuminate a media such that a charge distribution on the media matches the image from the imaging source.
  • the charge distribution distributes a marking material over the substrate such that the marking material distribution matches the image from the imaging source.
  • a signal is transmitted to recalibrate the printbar.
  • a signal may be generated upon each power up of the printbar, or more typically, the signal may be generated after an extended period of printing.
  • a signal to recalibrate the printbar is received, only one LED is switched on and all remaining LEDs are switched off in block 840.
  • a comparison circuit compares the output of photodetector with the detector match current stored in memory in block 844.
  • an ideal starting current is the calibration current for the LED, typically this calibration current was determined during printbar assembly or the last recalibration of the printbar.
  • the drive circuit increases the current to the LED in block 848 to increase the LED output.
  • the driver circuit decreases the drive current to the LED in block 852.
  • the drive current used becomes the new calibration current for the LED.
  • the new calibration current value replaces the calibration current value stored in memory.
  • block 860 it is determined if this is the last LED to be tested in the printbar. When it is not the last LED to be tested, the tested LED is turned off, and the next LED to be tested in the printbar is turned on in box 864. The procedure beginning with box 844 is then repeated with a corresponding photodetector for the next LED to be tested. The procedure continues until every LED in the printbar has been tested. In the event that the LEDs have reached a point that regardless of drive current, the LED cannot output signal sufficient to cause the photodetector to output sufficient current, a warning may be provided to the user that the printbar should be replaced. In order to facilitate understanding of the invention, a number of details have been provided.

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  • Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • Optics & Photonics (AREA)
  • General Engineering & Computer Science (AREA)
  • Toxicology (AREA)
  • General Health & Medical Sciences (AREA)
  • Health & Medical Sciences (AREA)
  • General Physics & Mathematics (AREA)
  • Theoretical Computer Science (AREA)
  • Printers Or Recording Devices Using Electromagnetic And Radiation Means (AREA)
  • Facsimile Heads (AREA)
  • Led Device Packages (AREA)
  • Led Devices (AREA)
  • Facsimile Scanning Arrangements (AREA)
  • Fax Reproducing Arrangements (AREA)

Claims (6)

  1. Druckbalken (104), umfassend:
    ein Druckbalkengehäuse (216) mit Innenwänden;
    eine Mehrzahl von Licht emittierenden Dioden (316, 320, 324) zur Bereitstellung von Licht für eine Abbildungsvorrichtung;
    einen Fotodetektor zum Erfassen der von jeder Licht emittierenden Diode in der Mehrzahl von Licht emittierenden Dioden ausgegebenen Leistung; und
    eine anpassbare Leistungsversorgung, die dafür ausgestaltet ist, eine Einzelanpassung von Leistung, die für jede Licht emittierende Diode in der Mehrzahl von Licht emittierenden Dioden bereitgestellt wird, zu ermöglichen, wobei die für die Licht emittierende Diode bereitgestellte Leistung auf Grundlage einer Rückkopplung bzw. Rückmeldung von dem Fotodetektor angepasst wird,
    dadurch gekennzeichnet, dass
    der Fotodetektor ein Streifenfotodetektor (404) ist, der entlang des Druckbalkens (104) parallel zu der Mehrzahl von Licht emittierenden Dioden verläuft, und
    der Streifenfotodetektor (404) in dem Druckbalkengehäuse (216) derart, dass Licht aus jeder Licht emittierenden Diode direkt auf den Streifendetektor auftrifft, oder derart,
    dass Licht aus jeder Licht emittierenden Diode auf den Streifendetektor nach einer Streuung an den Innenwänden des Druckbalkengehäuses (216) auftrifft, angeordnet ist.
  2. Druckbalken nach Anspruch 1, wobei der Fotodetektor in der Zeit gemultiplext wird, um die Ausgabe einer ersten Licht emittierenden Diode (316) in der Mehrzahl von Licht emittierenden Dioden zu einer ersten Zeit zu bestimmen und die Ausgabe einer zweiten Licht emittierenden Diode (320) in der Mehrzahl von Licht emittierenden Dioden zu einer zweiten Zeit zu bestimmen.
  3. Druckbalken nach Anspruch 1, wobei die anpassbare Leistungsversorgung die Menge von für die Licht emittierenden Dioden bereitgestelltem Strom ändert.
  4. Druckbalken nach Anspruch 1, des Weiteren umfassend:
    eine Speichervorrichtung zum Speichern eines Kalibrierungsstromes für jede Licht emittierende Diode, wobei der Kalibrierungsstrom derjenige Strom ist, der für die Licht emittierende Diode bereitgestellt wird, um zu bewirken, dass die Licht emittierende Diode eine vorbestimmte Lichtstärke an einer Fotorezeptorebene (232) ausgibt.
  5. Verfahren zur Kalibrierung eines Druckbalkens (104) in einem Drucker, umfassend die nachfolgenden Vorgänge:
    Einsetzen eines Druckbalkens (104) zum Ausgeben eines Bildes;
    in dem Druckbalken erfolgendes Bereitstellen einer Mehrzahl von Licht emittierenden Dioden (316, 320, 324) zur Bereitstellung von Licht für eine Abbildungsvorrichtung;
    Bestimmen, wann der Druckbalken (104) einer Neukalibrierung bedarf;
    an einem Fotodetektor, der in den Druckbalken (104) integriert ist, erfolgendes Erfassen der Ausgabe einer Licht emittierenden Diode in der Mehrzahl von Licht emittierenden Dioden und Anpassen eines für die Licht emittierende Diode bereitgestellten Stromes, bis die von dem Fotodetektor erfasste Lichtstärke zu einer während des Zusammensetzens des Druckbalkens bestimmten Referenzstärke passt,
    dadurch gekennzeichnet, dass
    der Fotodetektor ein Streifenfotodetektor (404) ist, der entlang des Druckbalkens (104) parallel zu der Mehrzahl von Licht emittierenden Dioden verläuft, und
    der Streifenfotodetektor (404) in dem Druckbalkengehäuse (216) derart, dass Licht aus jeder Licht emittierenden Diode direkt auf den Streifendetektor auftrifft, oder derart, dass Licht aus jeder Licht emittierenden Diode auf den Streifendetektor nach einer Streuung an den Innenwänden des Druckbalkengehäuses (216) auftrifft, angeordnet ist.
  6. Verfahren nach Anspruch 5, des Weiteren umfassend den nachfolgenden Vorgang:
    Ersetzen eines in einem Speicher gespeicherten Referenzstromwertes durch einen revidierten Referenzstromwert, wobei der revidierte Referenzstromwert den für die Licht emittierende Diode bereitgestellten neuen Strom angibt, der bewirkt, dass die von dem Fotodetektor erfasste Lichtstärke zu der während des Zusammensetzens des Druckbalkens bestimmten Referenzstärke passt.
EP02028810.6A 2001-12-26 2002-12-23 Verfahren und Vorrichtung zur Beleuchtungserkennung zur Verwendung bei LED-Druckbalken Expired - Fee Related EP1326198B1 (de)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US10/025,484 US6828538B2 (en) 2001-12-26 2001-12-26 Illumination detection method for LED printbars
US25484 2001-12-26

Publications (3)

Publication Number Publication Date
EP1326198A2 EP1326198A2 (de) 2003-07-09
EP1326198A3 EP1326198A3 (de) 2004-05-12
EP1326198B1 true EP1326198B1 (de) 2014-02-26

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US (1) US6828538B2 (de)
EP (1) EP1326198B1 (de)
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EP2842306B1 (de) 2012-04-24 2018-07-04 Hewlett-Packard Development Company, L.P. Drucksystem und betriebsverfahren
TWI477404B (zh) * 2012-06-08 2015-03-21 Nisho Image Tech Inc 發光裝置之光量補償檢查方法
JP5747929B2 (ja) * 2013-02-20 2015-07-15 コニカミノルタ株式会社 光書き込み装置および画像形成装置
KR20160005708A (ko) 2013-04-12 2016-01-15 카드랩 에이피에스 카드, 조립체, 상기 카드를 조립하는 방법 및 정보를 출력하는 방법
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JP2003266791A (ja) 2003-09-24
EP1326198A3 (de) 2004-05-12
US20030116694A1 (en) 2003-06-26
US6828538B2 (en) 2004-12-07
EP1326198A2 (de) 2003-07-09

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